U.S. patent number 8,903,048 [Application Number 14/080,575] was granted by the patent office on 2014-12-02 for radiographic imaging apparatus and control method for the same.
This patent grant is currently assigned to FUJIFILM Corporation. The grantee listed for this patent is FUJIFILM Corporation. Invention is credited to Naoto Iwakiri, Kouichi Kitano, Haruyasu Nakatsugawa, Naoyuki Nishino, Yasunori Ohta.
United States Patent |
8,903,048 |
Kitano , et al. |
December 2, 2014 |
Radiographic imaging apparatus and control method for the same
Abstract
An X-ray imaging apparatus includes an FPD and short-circuited
pixels. The FPD has pixels arranged in arrays for detecting an
X-ray image. The short-circuited pixels detect a radiation dose of
X-rays in the FPD. The X-ray imaging apparatus is changed over
between first and second operating modes. The first operating mode
is selected in case of combining with an X-ray generating apparatus
with communication compatibility, and performs an exposure control
for controlling a total radiation dose according to a detection
signal from the short-circuited pixels. The second operating mode
is selected in case of combining with an X-ray generating apparatus
with communication incompatibility, and performs control of start
synchronization for synchronizing operation of the FPD with the
emission start of X-rays according to a detection signal from the
short-circuited pixels. Thus, control of the X-ray imaging
apparatus is changed over appropriately.
Inventors: |
Kitano; Kouichi
(Ashigarakami-gun, JP), Nishino; Naoyuki
(Ashigarakami-gun, JP), Ohta; Yasunori
(Ashigarakami-gun, JP), Iwakiri; Naoto
(Ashigarakami-gun, JP), Nakatsugawa; Haruyasu
(Ashigarakami-gun, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
FUJIFILM Corporation |
Tokyo |
N/A |
JP |
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Assignee: |
FUJIFILM Corporation (Tokyo,
JP)
|
Family
ID: |
47601111 |
Appl.
No.: |
14/080,575 |
Filed: |
November 14, 2013 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20140072103 A1 |
Mar 13, 2014 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/JP2012/068672 |
Jul 24, 2012 |
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Foreign Application Priority Data
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Jul 26, 2011 [JP] |
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2011-163195 |
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Current U.S.
Class: |
378/115;
378/116 |
Current CPC
Class: |
A61B
6/542 (20130101); A61B 6/4233 (20130101); A61B
8/54 (20130101); A61B 6/4283 (20130101); A61B
6/56 (20130101) |
Current International
Class: |
A61B
6/00 (20060101) |
Field of
Search: |
;378/114-116,108,110,112,97 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2004-130058 |
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Apr 2004 |
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JP |
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2008-132216 |
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Jun 2008 |
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JP |
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2010-213917 |
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Sep 2010 |
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JP |
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2011-502699 |
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Jan 2011 |
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JP |
|
Other References
International Preliminary Report on Patentability and English
translation of the Written Opinion of the International Searching
Authority for Application No. PCT/JP2012/068672 dated Feb. 6, 2014
(Forms PCT/IB/338, PCT/IB/373, and PCT/ISA/237). cited by applicant
.
International Search Report issued in PCT/JP2012/068672, dated Aug.
28, 2012. cited by applicant.
|
Primary Examiner: Song; Hoon
Attorney, Agent or Firm: Birch, Stewart, Kolasch &
Birch, LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a Continuation of PCT International Application
No. PCT/JP2012/068672 filed on Jul. 24, 2012, which claims priority
under 35 U.S.C. .sctn.119(a) to Patent Application No. 2011-163195
filed in Japan on Jul. 26, 2011, all of which are hereby expressly
incorporated by reference into the present application.
Claims
What is claimed is:
1. A radiographic imaging apparatus for use with a radiation
generating apparatus for emitting radiation, comprising: an image
detector, having an imaging area in which plural pixels are
arranged in arrays for storing a signal charge according to a
radiation dose of said radiation upon receiving said radiation from
said radiation generating apparatus, for detecting a radiation
image by receiving radiation transmitted through an object; a
radiation detector for outputting a detection signal according to
said radiation dose, in order to detect an emission start of said
radiation from said radiation generating apparatus, and/or in order
to measure a total radiation dose of said radiation; a
communication interface for communicating with said radiation
generating apparatus; a mode selector for selectively setting one
of first and second operating modes; wherein said first operating
mode is used in case of combination with said radiation generating
apparatus with which said communication interface has communication
compatibility, for performing at least an exposure control for
measuring said total radiation dose according to said detection
signal from said radiation detector; said second operating mode is
used in case of combination with said radiation generating
apparatus with which said communication interface has communication
incompatibility, for performing at least a control of start
synchronization for detecting said emission start according to said
detection signal from said radiation detector and starting a
storage step of storing said signal charge of said image detector
in synchronism with said emission start; a controller for
controlling said image detector according to said one operating
mode selectively set by said mode selector.
2. A radiographic imaging apparatus as defined in claim 1, wherein
in said first operating mode, said controller starts said storage
step in synchronism with an emission start signal transmitted to
said communication interface by said radiation generating
apparatus.
3. A radiographic imaging apparatus as defined in claim 2, wherein
in said first operating mode, said controller measures said total
radiation dose by accumulating said detection signal from said
radiation detector, and when said total radiation dose reaches a
threshold, causes said communication interface to transmit a stop
signal to said radiation generating apparatus to stop emission of
said radiation.
4. A radiographic imaging apparatus as defined in claim 3, wherein
when said total radiation dose reaches said threshold, said
controller terminates said storage step of said image detector.
5. A radiographic imaging apparatus as defined in claim 1, wherein
in said second operating mode, said controller detects an emission
end of said radiation from said radiation generating apparatus
according to said detection signal from said radiation detector in
addition to said control of said start synchronization, and
terminates said storage step of said image detector in synchronism
with said emission end.
6. A radiographic imaging apparatus as defined in claim 1, wherein
in said second operating mode, said controller terminates said
storage step upon a lapse of a predetermined time after a start of
said storage step.
7. A radiographic imaging apparatus as defined in claim 2, wherein
in said first and second operating modes, said controller carries
out resetting in which a signal charge of said pixels is reset
after detecting said emission start and before starting said
storage step.
8. A radiographic imaging apparatus as defined in claim 1, wherein
in said first operating mode, said controller performs said control
of said start synchronization in addition to said exposure
control.
9. A radiographic imaging apparatus as defined in claim 1, wherein
said mode selector selects said operating modes according to manual
operation for mode selection.
10. A radiographic imaging apparatus as defined in claim 1, wherein
said mode selector detects communication compatibility or
incompatibility with said radiation generating apparatus, and
automatically selects said operating modes according to a result of
detection.
11. A radiographic imaging apparatus as defined in claim 1, further
comprising a notifier for notifying information as to which of said
first and second operating modes is selected.
12. A radiographic imaging apparatus as defined in claim 2, wherein
in said first operating mode, said emission start signal from said
radiation generating apparatus is constituted by a pulse wave, and
said communication interface notifies said controller of receiving
said emission start signal upon detecting an edge of said pulse
wave.
13. A radiographic imaging apparatus as defined in claim 1, wherein
said radiation detector is disposed in said imaging area.
14. A radiographic imaging apparatus as defined in claim 13,
wherein said radiation detector is disposed in each one of plural
partial areas defined by splitting said imaging area; said
controller changes over said partial areas for use between said
exposure control and said control of said start
synchronization.
15. A radiographic imaging apparatus as defined in claim 14,
wherein said plural partial areas include a central partial area
disposed at a center of said imaging area and a side partial area
disposed in a periphery of said central partial area; said
controller uses said central and side partial areas selectively in
said exposure control and said control of said start
synchronization.
16. A radiographic imaging apparatus as defined in claim 15,
wherein said controller changes a sensitivity of said radiation
detector in said partial areas for use in respectively said
exposure control and said control of said start
synchronization.
17. A radiographic imaging apparatus as defined in claim 13,
wherein said radiation detector is a short-circuited pixel where
one of said pixels is always short-circuited with a signal line for
reading out said signal charge from said pixel, for outputting said
signal charge to said signal line according to said radiation
dose.
18. A radiographic imaging apparatus as defined in claim 1, wherein
said image detector operates for motion imaging by receiving plural
radiation pulses of said radiation emitted successively by said
radiation generating apparatus; in said motion imaging, said
controller detects an edge of said radiation pulses according to
said detection signal from said radiation detector, and
synchronizes said storage step of said image detector with emission
of said radiation pulses.
19. A radiographic imaging apparatus as defined in claim 18,
wherein said controller measures said radiation dose per said
radiation pulses according to said detection signal from said
radiation detector, and controls an output gain of said signal
charge according to a result of measurement.
20. A control method for a radiographic imaging apparatus for use
with a radiation generating apparatus for emitting radiation, said
radiographic imaging apparatus including an image detector, having
an imaging area in which plural pixels are arranged in arrays for
storing a signal charge according to a radiation dose of said
radiation upon receiving said radiation from said radiation
generating apparatus, for detecting a radiation image by receiving
radiation transmitted through an object, a radiation detector for
outputting a detection signal according to said radiation dose, in
order to detect an emission start of said radiation from said
radiation generating apparatus, and/or in order to measure a total
radiation dose of said radiation, and a communication interface for
communicating with said radiation generating apparatus, said
control method comprising steps of: selectively setting one of
first and second operating modes; wherein said first operating mode
is used in case of combination with said radiation generating
apparatus with which said communication interface has communication
compatibility, for performing at least an exposure control for
measuring said total radiation dose according to said detection
signal from said radiation detector; said second operating mode is
used in case of combination with said radiation generating
apparatus with which said communication interface has communication
incompatibility, for performing at least a control of start
synchronization for detecting said emission start according to said
detection signal from said radiation detector and starting a
storage step of storing said signal charge of said image detector
in synchronism with said emission start; controlling said image
detector and said radiation detector according to said one
operating mode selectively set by said mode setting step.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radiographic imaging apparatus
for detecting a radiation image of an object, and a control method
for the radiographic imaging apparatus.
2. Description Related to the Prior Art
An X-ray imaging system is known in a medical field in use of
radiation, such as X-rays. The X-ray imaging system includes an
X-ray generating apparatus and an X-ray imaging apparatus. The
X-ray generating apparatus has an X-ray source for generating
X-rays. The X-ray imaging apparatus detects an X-ray image of image
information of an object by receiving X-rays transmitted through
the object after emission from the X-ray source. The X-ray source
is provided with an imaging condition inclusive of a tube current
and a tube voltage, the tube current determining a dose of X-rays
per unit time, the tube voltage determining energy spectrum of
X-rays. The imaging condition is determined for each event of
imaging according to a body part, age and the like of the object or
a body of examination with X-rays. The X-ray source emits X-rays
according to the imaging condition.
A newly suggested type of the X-ray imaging apparatus includes an
FPD (flat panel detector) or image detector in place of X-ray film
or imaging plate (IP) used conventionally (See U.S. Pat. Nos.
6,967,332, 7,235,789 and 7,507,970 (corresponding to JP-A
2004-130058)). The FPD includes a detection panel and a signal
processing circuit. The detection panel has an imaging area
including plural pixels and signal lines. The pixels store a signal
charge according to a radiation dose of X-rays. The signal lines
read the signal charge in connection with the pixels. The signal
processing circuit reads the stored signal charge form the pixels
as a voltage signal, and converts the voltage signal into image
data of a digital form. Thus, the X-ray image can be viewed
immediately after the imaging in the X-ray imaging apparatus
including the FPD.
In the detection panel, each of pixels in the imaging area is
constituted by a photo diode as a photoelectric conversion element,
and a TFT (thin film transistor). Scintillator (phosphor) is
provided in the imaging area for converting X-rays into visible
light. The TFT is a switching element for turning on and off
electric connection between the photo diode and a signal line, to
change over operation of the pixel. When the TFT is turned off, a
non-conductive state is created between the photo diode and the
signal line, to start a storage step in which a signal charge is
stored in the photo diode. When the TFT is turned on, a conductive
state is created between the photo diode and the signal line, to
start a readout step in which the signal charge is read from the
photo diode through the TFT and the signal line.
It is necessary with the X-ray imaging apparatus having the FPD to
perform control of start synchronization to start the storage step
in synchronism with the emission start of X-rays, unlike the X-ray
film or imaging plate (IP). A widely used example of the control of
start synchronization is a signal communication method in which a
sync signal is sent between the X-ray generating apparatus and the
X-ray imaging apparatus.
Examples of the control of start synchronization include not only
the signal communication method but an auto-detecting method
disclosed in U.S. Pat. Nos. 6,967,332, 7,235,789 and 7,507,970. In
the auto-detecting method, changes in the radiation dose of X-rays
emitted by the X-ray generating apparatus are monitored in the
X-ray imaging apparatus, to detect a time point of an emission
start of X-rays in a manner of auto-detection. The X-ray imaging
apparatus disclosed in U.S. Pat. Nos. 6,967,332, 7,235,789 and
7,507,970 includes detecting elements, disposed in addition to
normal pixels in the imaging area of the FPD, for detecting the
radiation dose of radiation to check a time point of the emission
start of X-rays. The control of start synchronization is performed
by use of the detecting elements in the auto-detecting method. It
is possible in the auto-detecting method to perform the control of
start synchronization without transmission of a sync signal between
the X-ray generating apparatus and the X-ray imaging apparatus.
Also, U.S. Pat. Nos. 6,967,332, 7,235,789 and 7,507,970 disclose
the use of the detecting elements for AEC or automatic exposure
control instead of the use for the control of start
synchronization.
In the AEC, a total radiation dose of X-rays received from the
X-ray generating apparatus is measured by the X-ray imaging
apparatus. The AEC is a control of an exposure of the X-ray image
by stopping emission of X-rays according to sending of a stop
signal to the X-ray generating apparatus upon reach of the total
radiation dose to a predetermined threshold. The AEC is performed
for suitably controlling the total radiation dose of X-rays. The
AEC makes it possible to prevent drop of image quality as an
optimum exposure is ensured. Also, overexposure to the object can
be prevented. Even in use of the X-ray film or imaging plate (IP)
distinct from the FPD, the AEC has been performed in the prior art
by combining the X-ray film or imaging plate (IP) with an exposure
control device referred to as a photo timer. As disclosed in U.S.
Pat. Nos. 6,967,332, 7,235,789 and 7,507,970, the detecting
elements in the FPD are used for the AEC to make a special exposure
control device unnecessary in a form discrete from the FPD.
JP-A 2008-132216 discloses the X-ray imaging apparatus in which the
signal communication method and the auto-detecting method of JP-A
2008-132216 can be used as methods for the control of start
synchronization. The X-ray imaging apparatus of JP-A 2008-132216
includes a wireless communication function for wirelessly
transmitting a sync signal in cooperation with the X-ray generating
apparatus. In a normal situation, the control of start
synchronization is performed in the signal communication method. If
a communication state of the wireless communication becomes poor,
or if failure in the wireless communication occurs, then an
emission start of X-rays is detected with the FPD in the
auto-detecting method, to perform the control of start
synchronization. In short, the X-ray imaging apparatus of JP-A
2008-132216 utilizes the signal communication method for the
control of start synchronization normally, but utilizes the
auto-detecting method exceptionally in the case of the poor
communication state.
In medical facilities with the X-ray imaging system, there has been
a recent trend of changing over from a conventional type of the
X-ray imaging apparatus with the X-ray film or imaging plate (IP)
to a new type of the X-ray imaging apparatus with the FPD. However,
the entirety of the X-ray imaging system is remarkably expensive. A
cost of updating is seriously high if the X-ray imaging system
inclusive of the X-ray generating apparatus is totally updated.
Thus, there is an idea of paying for introducing only the X-ray
imaging apparatus with the FPD, and combining this with the
existing type of the X-ray generating apparatus to update the X-ray
imaging system.
As described heretofore, the control of start synchronization is
required between the X-ray imaging apparatus and the X-ray
generating apparatus to use a new type of the X-ray imaging
apparatus having the FPD. A known type of the X-ray generating
apparatus has the communication function in connection with the
X-ray imaging apparatus, and a communication interface (standards
of a cable and connector, signal format, and the like) is
compatible with the communication interface of the X-ray imaging
apparatus. In the case of this communication compatibility between
the X-ray generating apparatus and the X-ray imaging apparatus, it
is possible to perform the control of start synchronization in a
normal type of the signal communication method.
In general, the signal communication method is more normally used
than the auto-detecting method, and is more reliable than the
latter as a method of the control of start synchronization. In the
case of communication compatibility with the X-ray generating
apparatus, it is preferable to perform the control of start
synchronization of the signal communication method in the X-ray
imaging apparatus.
However, it is likely that the X-ray generating apparatus of the
existing type does not have the communication function for
communicating with the X-ray imaging apparatus. Even if the
communication function exists, communication incompatibility is
likely to occur between the communication interface of the X-ray
generating apparatus and that of the X-ray imaging apparatus.
Communication is impossible between the X-ray generating apparatus
and the X-ray imaging apparatus, in which the control of start
synchronization according to the signal communication method cannot
be performed.
For this situation, the X-ray imaging apparatus in which the
control of start synchronization of the auto-detecting method is
possible according to U.S. Pat. Nos. 6,967,332, 7,235,789 and
7,507,970 and JP-A 2008-132216 can be used, so as to establish the
X-ray imaging system in combination of the X-ray generating
apparatus of a conventional type.
The AEC is a control on a condition of stopping emission of X-rays
by sending a stop signal from the X-ray imaging apparatus to the
X-ray generating apparatus. As emission of X-rays cannot be stopped
in the case of impossibility of communication with the X-ray
generating apparatus, effect of ensuring an optimum exposure of the
X-ray image, effect of overexposure to the object, and other effect
of the AEC cannot be obtained. Specifically, if the AEC is
performed in the X-ray imaging apparatus without communicability
with the X-ray generating apparatus, no stop of emission of X-rays
occurs, because the X-ray generating apparatus cannot receive a
stop signal even upon outputting the stop signal from the X-ray
imaging apparatus. On the other hand, it is likely in the X-ray
imaging apparatus that the readout step is started after the
storage step on a condition of stopping emission of X-rays with the
AEC. As the emission of X-rays continues even during the readout
step, noise may be caused to lower image quality of the X-ray
image. Also, X-rays continue being applied even after the end of
the storage step. X-rays not contributing to the X-ray image are
emitted. Thus, no effect of preventing overexposing the object can
be obtained.
Consequently, the combined use of the X-ray imaging apparatus with
the X-ray generating apparatus can be made appropriate in relation
to the control of start synchronization and the AEC of the X-ray
imaging apparatus according to communication compatibility or
incompatibility with the X-ray generating apparatus.
Although U.S. Pat. Nos. 6,967,332, 7,235,789 and 7,507,970 disclose
both of the control of start synchronization and the AEC for the
auto-detecting method by use of the detecting elements of the FPD,
there is no disclosure as to which of the control of start
synchronization and the AEC should be performed by use of the
detecting elements.
Although JP-A 2008-132216 discloses the signal communication method
and the auto-detecting method in relation to the control of start
synchronization, there is no suggestion of the AEC.
SUMMARY OF THE INVENTION
In view of the foregoing problems, an object of the present
invention is to provide a radiographic imaging apparatus in which
control can be performed suitably according to communication
compatibility or incompatibility with the X-ray generating
apparatus in relation to the control of start synchronization and
the AEC (automatic exposure control), and a control method for the
radiographic imaging apparatus.
In order to achieve the above and other objects and advantages of
this invention, a radiographic imaging apparatus for use with a
radiation generating apparatus for emitting radiation is provided.
An image detector has an imaging area in which plural pixels are
arranged in arrays for storing a signal charge according to a
radiation dose of the radiation upon receiving the radiation from
the radiation generating apparatus, for detecting a radiation image
by receiving radiation transmitted through an object. A radiation
detector outputs a detection signal according to the radiation
dose, in order to detect an emission start of the radiation from
the radiation generating apparatus, and/or in order to measure a
total radiation dose of the radiation. A communication interface
communicates with the radiation generating apparatus. A mode
selector selectively sets one of first and second operating modes.
The first operating mode is used in case of combination with the
radiation generating apparatus with which the communication
interface has communication compatibility, for performing at least
an exposure control for measuring the total radiation dose
according to the detection signal from the radiation detector. The
second operating mode is used in case of combination with the
radiation generating apparatus with which the communication
interface has communication incompatibility, for performing at
least a control of start synchronization for detecting the emission
start according to the detection signal from the radiation detector
and starting a storage step of storing the signal charge of the
image detector in synchronism with the emission start. A controller
controls the image detector according to the one operating mode
selectively set by the mode selector.
In the first operating mode, the controller starts the storage step
in synchronism with an emission start signal transmitted to the
communication interface by the radiation generating apparatus.
In the first operating mode, the controller measures the total
radiation dose by accumulating the detection signal from the
radiation detector, and when the total radiation dose reaches a
threshold, causes the communication interface to transmit a stop
signal to the radiation generating apparatus to stop emission of
the radiation.
When the total radiation dose reaches the threshold, the controller
terminates the storage step of the image detector.
In another preferred embodiment, in the second operating mode, the
controller detects an emission end of the radiation from the
radiation generating apparatus according to the detection signal
from the radiation detector in addition to the control of the start
synchronization, and terminates the storage step of the image
detector in synchronism with the emission end.
In one preferred embodiment, in the second operating mode, the
controller terminates the storage step upon a lapse of a
predetermined time after a start of the storage step.
In still another preferred embodiment, in the first and second
operating modes, the controller carries out resetting in which a
signal charge of the pixels is reset after detecting the emission
start and before starting the storage step.
In one preferred embodiment, in the first operating mode, the
controller performs the control of the start synchronization in
addition to the exposure control.
In another preferred embodiment, the mode selector selects the
operating modes according to manual operation for mode
selection.
In one preferred embodiment, the mode selector detects
communication compatibility or incompatibility with the radiation
generating apparatus, and automatically selects the operating modes
according to a result of detection.
Furthermore, a notifier for notifying information as to which of
the first and second operating modes is selected.
In the first operating mode, the emission start signal from the
radiation generating apparatus is constituted by a pulse wave, and
the communication interface notifies the controller of receiving
the emission start signal upon detecting an edge of the pulse
wave.
The radiation detector is disposed in the imaging area.
The radiation detector is disposed in each one of plural partial
areas defined by splitting the imaging area. The controller changes
over the partial areas for use between the exposure control and the
control of the start synchronization.
The plural partial areas include a central partial area disposed at
a center of the imaging area and a side partial area disposed in a
periphery of the central partial area. The controller uses the
central and side partial areas selectively in the exposure control
and the control of the start synchronization.
The controller changes a sensitivity of the radiation detector in
the partial areas for use in respectively the exposure control and
the control of the start synchronization.
The radiation detector is a short-circuited pixel where one of the
pixels is always short-circuited with a signal line for reading out
the signal charge from the pixel, for outputting the signal charge
to the signal line according to the radiation dose.
The image detector operates for motion imaging by receiving plural
radiation pulses of the radiation emitted successively by the
radiation generating apparatus. In the motion imaging, the
controller detects an edge of the radiation pulses according to the
detection signal from the radiation detector, and synchronizes the
storage step of the image detector with emission of the radiation
pulses.
The controller measures the radiation dose per the radiation pulses
according to the detection signal from the radiation detector, and
controls an output gain of the signal charge according to a result
of measurement.
Also, a control method for a radiographic imaging apparatus for use
with a radiation generating apparatus for emitting radiation is
provided, the radiographic imaging apparatus including an image
detector, having an imaging area in which plural pixels are
arranged in arrays for storing a signal charge according to a
radiation dose of the radiation upon receiving the radiation from
the radiation generating apparatus, for detecting a radiation image
by receiving radiation transmitted through an object, a radiation
detector for outputting a detection signal according to the
radiation dose, in order to detect an emission start of the
radiation from the radiation generating apparatus, and/or in order
to measure a total radiation dose of the radiation, and a
communication interface for communicating with the radiation
generating apparatus. The control method includes a step of
selectively setting one of first and second operating modes. The
first operating mode is used in case of combination with the
radiation generating apparatus with which the communication
interface has communication compatibility, for performing at least
an exposure control for measuring the total radiation dose
according to the detection signal from the radiation detector. The
second operating mode is used in case of combination with the
radiation generating apparatus with which the communication
interface has communication incompatibility, for performing at
least a control of start synchronization for detecting the emission
start according to the detection signal from the radiation detector
and starting a storage step of storing the signal charge of the
image detector in synchronism with the emission start. The image
detector and the radiation detector are controlled according to the
one operating mode selectively set by the mode setting step.
In the present invention, control can be performed suitably
according to communication compatibility or incompatibility with
the X-ray generating apparatus in relation to the control of start
synchronization and the AEC (automatic exposure control).
BRIEF DESCRIPTION OF THE DRAWINGS
The above objects and advantages of the present invention will
become more apparent from the following detailed description when
read in connection with the accompanying drawings, in which:
FIG. 1 is an explanatory view schematically illustrating an X-ray
imaging system having an X-ray generating apparatus having
communication compatibility with an X-ray imaging apparatus;
FIG. 2 is a perspective view of appearance illustrating the X-ray
imaging apparatus;
FIG. 3 is an explanatory view illustrating an FPD;
FIG. 4 is an explanatory view illustrating changeover between first
and second operating modes in a first embodiment;
FIG. 5 is an explanatory view illustrating steps of the first
operating mode in the first embodiment;
FIG. 6 is an explanatory view illustrating steps of the second
operating mode in the first embodiment;
FIG. 7 is a flow chart illustrating a control of the FPD in the
first operating mode in the first embodiment;
FIG. 8 is an explanatory view schematically illustrating an X-ray
imaging system having an X-ray generating apparatus incompatible
with the X-ray imaging apparatus for communication
compatibility;
FIG. 9 is a flow chart illustrating a control of the FPD in the
second operating mode in the first embodiment;
FIG. 10 is an explanatory view illustrating steps of the first
operating mode in a second embodiment;
FIG. 11 is an explanatory view illustrating steps of the second
operating mode in the second embodiment;
FIG. 12 is an explanatory view illustrating a variant of the first
operating mode in the second embodiment;
FIG. 13 is an explanatory view illustrating a variant of the second
operating mode in the second embodiment;
FIG. 14 is an explanatory view illustrating an imaging area of the
FPD of third and fourth embodiments;
FIG. 15 is an explanatory view illustrating steps of motion imaging
of a fifth embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) OF THE PRESENT
INVENTION
[First Embodiment]
In FIG. 1, an X-ray imaging system 10 is constituted by assembling
an X-ray imaging apparatus 12 in an X-ray imaging system, which is
conventional and has an X-ray generating apparatus 11 and an
imaging stand 22. The X-ray generating apparatus 11 is communicable
with an external device. The imaging stand 22 is so formed that a
film cassette or IP cassette can be mounted thereon. The X-ray
imaging apparatus 12 includes an X-ray imaging assembly 21 (imaging
device), a controller 23 (imaging controller) and a console unit
24.
The X-ray generating apparatus 11 includes an X-ray source 13, a
radiation source control assembly 14 (control unit) and a radiation
switch 15. The radiation source control assembly 14 controls the
X-ray source 13. The X-ray source 13 includes an X-ray tube 13a and
a radiation field limiting device (collimator) 13b. The X-ray tube
13a emits X-rays. The radiation field limiting device 13b limits an
irradiation field of X-rays emitted by the X-ray tube 13a.
The X-ray tube 13a has a cathode and an anode (target), the cathode
having filaments for emitting thermal electrons, the anode
undergoing collision of the thermal electrons from the cathode to
emit X-rays. The radiation field limiting device 13b includes four
metal lead plates, which shield X-rays, are arranged in a frame
form, and have an emitting opening for passing X-rays. The metal
lead plates are shifted to change the sizes of the emitting opening
to limit the radiation field. The four metal lead plates are
combined in two pairs. Metal lead plates in each of the pairs are
opposed to one another. The pairs are arranged in two directions
perpendicular with one another to define the quadrilateral emitting
opening.
The radiation source control assembly 14 includes a high voltage
source 14a, a radiation source control device 14b and a
communication device 14c. The high voltage source 14a supplies the
X-ray source 13 with high voltage. The radiation source control
device 14b controls a tube voltage, tube current and irradiation
time of X-rays. The tube voltage is a value for determining energy
spectrum or quality of X-rays emitted by the X-ray source 13. The
tube current is a value for determining a radiation dose per unit
time. The communication device 14c is communicable with the
controller 23 in a wired manner or wirelessly. The high voltage
source 14a boosts an input voltage with a transformer, generates
the tube voltage as a high voltage, and supplies the X-ray source
13 with drive power by use of a high voltage cable. An imaging
condition including the tube voltage, tube current and emission
stop condition is manually set in the radiation source control
device 14b by a radiology technician or operator with an input
panel of the radiation source control assembly 14.
The radiation switch 15 is connected to the radiation source
control assembly 14 by a signal cable. The radiation switch 15 is a
two-step switch operable by the radiology technician, generates a
warmup start signal for starting warming up the X-ray source 13
upon a first step of depression, and generates an emission start
signal for the X-ray source 13 upon a second step of depression.
Those signals are input to the radiation source control assembly 14
by a signal cable.
The radiation source control device 14b controls operation of the
X-ray source 13 according to a control signal from the radiation
switch 15. Upon receiving an emission start signal from the
radiation switch 15, the radiation source control assembly 14
instructs the X-ray source 13 to start, and starts supplying power.
Thus, the X-ray source 13 starts emission. Upon starting the supply
of power, the radiation source control device 14b causes the
communication device 14c to send an emission start signal to the
controller 23 as a sync signal expressing an emission start of
X-rays. The emission start signal is used for a control of start
synchronization for synchronizing operation of the X-ray imaging
assembly 21 with a time point of the emission start of X-rays from
the X-ray generating apparatus 11.
If the irradiation time is specified as an emission stop condition
set according to the imaging condition, the radiation source
control device 14b operates a timer upon starting the power supply,
and starts measuring the irradiation time of X-rays. When the
irradiation time set according to the imaging condition elapses,
the radiation source control device 14b sends a stop command to the
X-ray source 13 to stop the power supply. The X-ray source 13 stops
the emission of X-rays upon receiving the stop command. If priority
to a stop signal from an external device is specified as an
emission stop condition set according to the imaging condition, the
radiation source control device 14b outputs a stop command upon
inputting the stop signal from the controller 23 to the
communication device 14c, to stop the power supply.
The imaging stand 22 has a slot in which a film cassette or IP
cassette is mounted removably, and is so positioned that its
receiving surface for receiving X-rays is opposed to the X-ray
source 13. Note that the example of the imaging stand 22 is a stand
where the object H is imaged in an erect orientation. However, a
table on which the object H is laid horizontally may be used in
place of the imaging stand 22.
The X-ray imaging apparatus 12 is constituted by the X-ray imaging
assembly 21, the controller 23 and the console unit 24. The X-ray
imaging assembly 21 includes a flat panel detector 36 (FPD as image
detector) (See FIG. 3) and a portable housing for containing the
flat panel detector 36, and is a portable type of radiographic
imaging assembly for receiving X-rays passed through a body
(object) H upon emission from the X-ray source 13, to detect an
X-ray image of the body H. The X-ray imaging assembly 21 has the
flat housing of which a plane shape is substantially quadrilateral,
and has a plane size as large as a film cassette or IP cassette, so
that the X-ray imaging assembly 21 is mountable on the imaging
stand 22.
The controller 23 includes a communication interface 23a and an
imaging control unit 23b. The communication interface 23a
communicates with the X-ray generating apparatus 11, the X-ray
imaging assembly 21 and the console unit 24 in a wired or wireless
manner. The imaging control unit 23b controls the X-ray imaging
assembly 21 by use of the communication interface 23a. The imaging
control unit 23b transmits information of an imaging condition to
the X-ray imaging assembly 21 to condition the signal processing in
the flat panel detector 36, and also receives a sync signal from
the X-ray generating apparatus 11 to synchronize the emission of
the X-ray source 13 with the storage step of the flat panel
detector 36. The imaging control unit 23b performs the sync control
between the X-ray source 13 and the flat panel detector 36 by
sending the sync signal to the X-ray imaging assembly 21. Also,
image data output by the X-ray imaging assembly 21 is received by
the imaging control unit 23b with the communication interface 23a,
and then sent to the console unit 24.
The console unit 24 receives information of an examination request
of the patient, such as sex, age, body part, purpose of imaging,
and the like, and causes the display panel to display the
information of the examination request. The examination request
information is originally supplied by an outer system for managing
patient information or diagnosis information, such as the HIS
(Hospital Information System) and RIS (Radiography Information
System). Also, the examination request information can be input by
an operator or technician manually. He or she observes the
examination request information on the display panel, and
selectively determines an imaging condition according to the same
by viewing images on the console unit 24.
The console unit 24 sends the imaging condition to the controller
23, and processes data of an X-ray image output by the controller
23 in image processing of various functions, such as gamma
correction, frequency processing and the like. The X-ray image
after the image processing is displayed on a display panel of the
console unit 24. The data of the X-ray image is stored in a data
storage device, such as a hard disk or memory in the console unit
24, or an image storage server in the network connection with the
console unit 24.
As illustrated in FIG. 2, the X-ray imaging assembly 21 has a
housing 25 of which a quadrilateral upper surface is a receiving
surface of radiation. The housing 25 includes a top panel 26 with
the receiving surface and a housing shell 27 for constituting
elements other than the top panel 26. For example, the top panel 26
is constituted by carbon and the like. The housing shell 27 is
constituted by metal, resin and the like. Therefore, absorption of
X-rays with the top panel 26 is suppressed. Strength of the housing
shell 27 is ensured.
An indicator 28 is disposed on an upper surface of the housing 25
as a notifier for notifying an operation state of the X-ray imaging
assembly 21 and the like. The indicator 28 includes, for example, a
plurality of light emitting devices, and indicates various data by
combining illuminating states of the light emitting devices, such
as operation states, operating modes, available performance of a
battery and the like of the X-ray imaging assembly 21. Examples of
the operation states are "ready state" as standby for imaging, and
"state during data transmission" for transmitting image data after
the imaging. Examples of the operating modes are a "first operating
mode" for use in case of combining the X-ray imaging assembly 21
with an X-ray generating apparatus in communication compatibility,
and a "second operating mode" for use in case of combining the
X-ray imaging assembly 21 with an X-ray generating apparatus in
communication incompatibility. The first and second operating modes
will be described later in detail. The indicator 28 may be a
display device such as an LCD. Note that a function of the
indicator 28 may be incorporated in the console unit 24.
The flat panel detector 36 is disposed in the housing 25 of the
X-ray imaging assembly 21, opposed to a receiving surface, for
detecting an X-ray image as an image detector. The flat panel
detector 36 is an indirect conversion type, and includes a
scintillator 29 and a detection panel 30. The scintillator 29
converts X-rays into visible light. The detection panel 30
photoelectrically detects the visible light converted by the
scintillator 29. The flat panel detector 36 is a type of
"Irradiation Side Sampling (ISS)" in which the detection panel 30
is disposed on a side of the scintillator 29 on the receiving
surface. Note that the flat panel detector 36 may be a type of
"Penetration Side Sampling (PSS)" in which disposition of the
scintillator 29 and the detection panel 30 is reversed.
Electronic circuits 31, a battery 32 and a communication interface
33 are disposed in the housing 25 on one end thereof along a
transverse direction of the receiving surface. The electronic
circuits 31 operate for controlling the flat panel detector 36, and
are protected by a material radiopaque to X-rays in order to
prevent electronic elements from being damaged with X-rays. The
battery 32 is contained in the housing 25 in a chargeable and
removable manner, and supplies power to the flat panel detector 36,
the electronic circuits 31 and the communication interface 33. The
communication interface 33 communicates with the controller 23 in a
wired manner or wirelessly.
In FIG. 3, the flat panel detector 36 includes the detection panel
30, a gate driver 39, a signal processing circuit 40 and a control
unit 41. The signal processing circuit 40 and the control unit 41
constitute the electronic circuits 31. The detection panel 30 has a
TFT active matrix substrate, and an imaging area 38 defined on the
substrate and constituted by plural pixels 37 for storing a signal
charge according to a radiation dose of X-rays. The gate driver 39
drives the pixels 37 and controls the readout step of the signal
charge. The signal processing circuit 40 outputs digital data by
conversion of the signal charge read from the pixels 37. The
control unit 41 controls the gate driver 39 and the signal
processing circuit 40 to control operation of the flat panel
detector 36. The communication interface 33 is connected to the
control unit 41 for communication with the controller 23 in a wired
or wireless manner. The pixels 37 are arranged in a matrix form of
n arrays (x direction) and m columns (y direction) in a
two-dimensional manner at a predetermined pitch.
The flat panel detector 36 has scintillator (not shown) for
converting X-rays to visible light, and is an indirect conversion
type in which the visible light from the scintillator is
photoelectrically converted with the pixels 37. The scintillator is
opposed fully to the imaging area 38 where the pixels 37 are
arranged. The scintillator is constituted by phosphor formed from
cesium iodide (CsI) or GOS (gadolinium oxysulfide). Also, the flat
panel detector can be a direct conversion type in which a
conversion layer of amorphous selenium and the like directly
converts X-rays into electric charge.
Each of the pixels 37 includes a photo diode 42, a capacitor (not
shown) and a thin film transistor 43 (TFT) as a switching element.
The photo diode 42 is a photoelectric conversion element for
generating charge (electron-hole pairs) upon entry of visible
light. The capacitor stores the charge generated by the photo diode
42.
The photo diode 42 has a structure including a semiconductor layer
such as a-Si (amorphous silicon), for example, of the PIN type, and
upper and lower electrodes formed on the semiconductor layer. The
TFT 43 is connected to the lower electrode of the photo diode 42. A
bias line (not shown) is connected to the upper electrode.
A bias voltage is applied to an upper electrode of the photo diode
42 for all the pixels 37 in the imaging area 38 through a bias
line. An electric field is created in the semiconductor layer in
the photo diode 42 by the application of the bias voltage. Charge
generated in the semiconductor layer by the photoelectric
conversion (electron-hole pairs) is moved to the upper and lower
electrodes of which one has a positive polarity and the other has a
negative polarity. The charge is stored in the capacitor.
The TFTs 43 have electrodes of a gate, source and drain. A scan
line 47 is connected with the gate of the TFTs 43. A signal line 48
is connected with the source. Each of the photo diodes 42 is
connected with the drain. The scan lines 47 and the signal lines 48
are disposed in a form of a grating. A number of the scan lines 47
is n or the array number of the pixels 37 in the imaging area 38.
The scan lines 47 are common lines connected to the pixels 37 of
the arrays. A number of the signal lines 48 is m or the column
number of the pixels 37. The signal lines 48 are common lines
connected to the pixels 37 of the arrays. The scan lines 47 are
connected to the gate driver 39. The signal lines 48 are connected
to the signal processing circuit 40.
The gate driver 39 drives the TFTs 43 for operation of the storage
step, readout step and reset step. In the storage step, a signal
charge according to the radiation dose of X-rays is stored in the
pixels 37. In the readout step, the signal charge is read from the
pixels 37. In the reset step, the charge stored in the pixels 37 is
reset. The control unit 41 controls time points of start of the
storage step, readout step and reset step carried out by the gate
driver 39.
In the storage step, the TFTs 43 are in a turn-off state. During
this period, a signal charge is stored in the pixels 37. In the
readout step, gate pulses G1-Gn for driving the TFTs 43 of a common
array together are generated by the gate driver 39, and activate
the scan lines 47 serially one array after another, to turn on the
TFTs 43 by one array in connection with the scan lines 47.
When the TFTs 43 of one array come to be in a turn-on state, the
signal charge stored in respectively the pixels 37 of the one array
is input to the signal processing circuit 40 through the signal
lines 48. In the signal processing circuit 40, the signal charge of
the one array is converted into voltage and output. An output
voltage according to respectively the signal charge is read as
voltage signals D1-Dm. The voltage signals D1-Dm of the analog form
are converted into digital data so that image data is created as
digital pixel values expressing density of respectively the pixels
of the one array. The image data is output to a memory 56 contained
in the housing of the X-ray imaging assembly 21.
A dark current is generated in the semiconductor layer of the photo
diodes 42 irrespective of entry of X-rays. A dark current charge as
charge according to the dark current is stored in the capacitor
owing to application of the bias voltage. The dark current creates
a noise component in the image data. Resetting is carried out for
eliminating the dark current. In the resetting, the dark current
generated at the pixels 37 is discharged from the pixels 37 through
the signal lines 48.
An example of the method of the resetting is sequential resetting
in which the pixels 37 are reset by one array. In a manner similar
to the readout step of a signal charge, the gate driver 39
successively sends gate pulses G1-Gn to the scan lines 47, and
turns on the TFTs 43 of the pixels 37 by one array. While each of
the TFTs 43 is turned on, a dark current charge from the pixel 37
flows to the signal processing circuit 40 through the signal line
48.
As a difference of the resetting from the readout step, there is no
readout step of an output voltage according to the dark current
charge in the signal processing circuit 40. The control unit 41
outputs a reset pulse RST to the signal processing circuit 40 in
synchronism with each of the gate pulses G1-Gn. Upon inputting the
reset pulse RST to the signal processing circuit 40, reset switches
49a of integrating amplifiers 49 to be described later are turned
on, to reset the input dark current charge.
Instead of the sequential resetting, the simultaneous resetting and
the total pixel resetting can be used. In the simultaneous
resetting, pixels are grouped in plural groups each of which is
constituted by a predetermined number of arrays of pixels. Pixels
of each of the groups are reset in the sequential resetting, to
discharge the dark current charge simultaneously from the arrays of
the various groups. In the total pixel resetting, a gate pulse is
input for all of the arrays to discharge the dark current charge of
all the pixels simultaneously. According to the simultaneous
resetting and the total pixel resetting, it is possible to quicken
reset operation.
The signal processing circuit 40 includes the integrating
amplifiers 49, an MUX 50 (multiplexer) and an A/D converter 51. The
integrating amplifiers 49 are connected with the signal lines
discretely from one another. Each of the integrating amplifiers 49
includes an operational amplifier, and a capacitor connected
between input and output terminals of the operational amplifier.
Each of the signal lines 48 is connected with a first one of the
input terminals of the operational amplifier. A second one of the
input terminals of the integrating amplifier 49 is grounded (GND).
The integrating amplifiers 49 accumulate signal charge input by the
signal lines 48, and convert the charge into voltage signals D1-Dm
as outputs.
Output terminals of the integrating amplifiers 49 of respective
columns are connected to the MUX 50 by amplifiers (not shown) and a
sample-hold circuit (not shown), the amplifiers amplifying the
voltage signals D1-Dm, the sample-hold circuit holding the voltage
signals D1-Dm. The MUX 50 selects one of the amplifier integrators
49 from each one of their columns in parallel, so that the voltage
signals D1-Dm output by the selected amplifier integrators 49 are
input to the A/D converter 51 serially. The A/D converter 51
converts the voltage signals D1-Dm in an analog form to digital
pixel values according to their signal level.
In the readout step for the signal charge after the storage step,
the TFTs 43 are turned on by gate pulses one array after another.
The signal charge stored in capacitors of the pixels 37 of
respective columns in the arrays is input to the integrating
amplifiers 49 by the signal lines 48.
When the voltage signals D1-Dm of the one array are output by the
integrating amplifiers 49, the control unit 41 outputs a reset
pulse (reset signal) to the integrating amplifiers 49 and turns on
the reset switches 49a of the same. The signal charge of the one
array stored in the integrating amplifiers 49 is reset. Upon the
resetting, a gate pulse of a succeeding array is output by the gate
driver 39, to start reading the signal charge of the pixels 37 of
the succeeding array. Those steps are repeated successively to read
the signal charge of the pixels 37 of all the arrays.
When the readout step of all the arrays is completed, image data of
an X-ray image of one frame is written to the memory 56. The image
data written to the memory 56 is processed in image correction,
such as offset correction and sensitivity correction. In the offset
correction, an offset component is eliminated as a fixed pattern
noise created by a specificity and environment of the flat panel
detector 36. In the sensitivity correction, errors in the
sensitivity of the photo diode 42 of the pixels 37 and errors in
the output characteristic are corrected. Image data are read from
the memory 56, output to the controller 23, and transmitted to the
console unit 24. Thus, the X-ray image of the object H is
detected.
In addition to the function of image detection, the flat panel
detector 36 has a function of detecting a radiation dose of X-rays
emitted by the X-ray source 13 for use in sync control with the
X-ray generating apparatus 11 and exposure control of an X-ray
image. As hatched in FIG. 3, short-circuited pixels 62 are provided
in the imaging area 38 of the flat panel detector 36 as a radiation
detector for detecting a radiation dose of X-rays. Although only
one of the short-circuited pixels 62 is depicted in FIG. 3, a
plurality of the short-circuited pixels 62 are present actually,
and disposed on the entirety of the imaging area 38 discretely from
one another. The number of the short-circuited pixels 62 is, for
example, approximately 1% as high as the number of the pixels 37.
Turning on and off of the TFTs 43 causes turning on and off of
electrical connection of the pixels 37 with the signal lines 48. In
contrast, the short-circuited pixels 62 are always short-circuited
with the signal lines 48.
The short-circuited pixels 62 are structurally similar to the
pixels 37, and have the photo diode 42 and the TFTs 43. The photo
diode 42 generates a signal charge according to a radiation dose of
X-rays. A structural difference of the short-circuited pixels 62
from the pixels 37 is a short-circuited form between the source and
drain of the TFTs 43 by wiring. A switching function of the TFTs 43
of the short-circuited pixels 62 is suppressed. Thus, the signal
charge generated by the photo diode 42 of the short-circuited
pixels 62 always flows to the signal lines 48, and is input to the
integrating amplifiers 49. Note that it is possible directly to
connect the photo diode 42 to the signal lines 48 without providing
the TFTs 43 at the short-circuited pixels 62 and instead of wiring
between the source and drain of the TFTs 43 of the short-circuited
pixels 62.
The control unit 41 measures a radiation dose of X-rays applied by
the X-ray source 13 to the flat panel detector 36 according to an
output of the short-circuited pixels 62. The control unit 41
selects one of the integrating amplifiers 49 to which a signal
charge is input from the short-circuited pixels 62 by use of the
MUX 50, and reads a voltage signal of the integrating amplifiers 49
as an output voltage Vout of the short-circuited pixels 62. The
control unit 41 resets the integrating amplifiers 49 upon reading
the output voltage Vout at one time. During the storage step, the
control unit 41 repeats the readout step of the output voltage Vout
at a very short period relative to irradiation time of X-rays, so
as to monitor changes in the intensity of X-rays being applied.
The control unit 41 converts the value of the output voltage Vout
into digital data, and writes the same to the memory 56. The
control unit 41 monitors a change in a radiation dose of X-rays
emitted by the X-ray source 13 according to a change with time in
the output voltage Vout stored in the memory 56, and can detect
time points of the emission start and emission end of X-rays from
the X-ray generating apparatus 11.
Also, the control unit 41 can measure a total radiation dose of
X-rays applied by the X-ray source 13 to the flat panel detector 36
according to an output of the short-circuited pixels 62. After
starting emission of X-rays, the control unit 41 reads the output
voltage Vout of the short-circuited pixels 62 at a short interval
in a manner similar to the above-described detection of the time
point of the emission start, and measures the total radiation dose
of X-rays by accumulating the output voltage Vout.
Thus, detection of time points of the emission start and emission
end of X-rays with the short-circuited pixels 62 enables the X-ray
imaging assembly 21 to perform sync control for synchronizing
operation of the X-ray imaging assembly 21 with the time points of
the emission start and emission end of the X-ray generating
apparatus 11, without communication of a sync signal with the X-ray
generating apparatus 11. Also, it is possible with the
short-circuited pixels 62 to perform exposure control to control an
exposure amount of an X-ray image appropriately by measuring a
total radiation dose of X-rays.
The X-ray imaging assembly 21 is provided with two operating modes,
namely, a first operating mode for utilizing the short-circuited
pixels 62 in the sync control and a second operating mode for
utilizing the short-circuited pixels 62 in the exposure control.
The control unit 41 has a function for mode changeover between the
two operating modes.
The first operating mode is a mode for use in case of combination
with the X-ray generating apparatus 11 having communication
compatibility with the communication interface 23a. The second
operating mode is a mode for use in case of combination with the
X-ray generating apparatus 11 having communication incompatibility
with the communication interface 23a.
As illustrated in the flow chart of FIG. 4, the first operating
mode is selected as an operating mode of the X-ray imaging assembly
21 if the X-ray generating apparatus 11 is communicable with the
X-ray imaging assembly 21. Also, if the X-ray generating apparatus
11 is not communicable with the X-ray imaging assembly 21, the
second operating mode is selected as an operating mode of the X-ray
imaging assembly 21. Note that the case where the X-ray generating
apparatus 11 is not communicable with the X-ray imaging assembly 21
may be incompatibility of an interface (standard of cable or
connector, format of the sync signal, or the like) for the sync
control between the X-ray generating apparatus 11 and the X-ray
imaging assembly 21, or lack of a communicating function in the
X-ray generating apparatus 11, or the like.
Changeover between the first and second operating modes is carried
out according to manual operation for the mode selection. Examples
of manual mode selection are initializing operation and mode
selecting operation. In the initializing operation, a service
operator operates the X-ray imaging apparatus 12 at the time of
newly installing the X-ray imaging apparatus 12 inclusive of the
X-ray imaging assembly 21. In the mode selecting operation, a user
inputs with the console unit 24 after installation of the X-ray
imaging apparatus 12. Information of the mode selection is stored
in an internal memory of the control unit 41. The X-ray imaging
assembly 21 operates in the selected mode if there is no change in
the mode selection.
If the X-ray generating apparatus 11 for combination with the X-ray
imaging assembly 21 is single, no further change of the mode is
required subsequently after selecting the mode in the initial
setting at the time of installation. If there are a plurality of
X-ray generating apparatuses 11 for combination with the X-ray
imaging assembly 21, changes in the mode may be required for each
of the X-ray generating apparatuses 11 for the combination. It is
preferable to operate for the mode selection at the console unit
24.
Instead of or in addition to manual operation of the mode
selection, it is possible to detect communication compatibility or
incompatibility with the X-ray generating apparatus 11 so that the
mode can be changed over automatically according to a result of the
detection. For example, the communication compatibility or
incompatibility with the X-ray generating apparatus 11 is detected
by the control unit 41 or the imaging control unit 23b. To this
end, the communication interface 23a or 33 sends a test signal to
the X-ray generating apparatus 11 and determines existence or
non-existence of a response from the same.
The X-ray imaging assembly 21 causes the indicator 28 to display
the operating mode selected by the manipulation of mode selection
or automatic changeover of the mode. Thus, a user can check the
selected operating mode according to appearance of the X-ray
imaging assembly 21.
FIG. 5 illustrates a total radiation dose of X-rays and an
operation state of the flat panel detector 36 in the case of
operating the X-ray imaging assembly 21 in the first operating
mode, the flat panel detector 36 being controlled according to the
total radiation dose. The radiation dose of X-rays is in a shape of
substantially a trapezoid in a graph of which time is taken on a
horizontal axis and the radiation dose (output voltage Vout) of
X-rays is taken on a vertical axis. When the X-ray source 13 starts
emitting X-rays upon receiving a start command, a radiation dose of
X-rays gradually increases, and comes up to a peak value according
to a tube current set in the imaging condition, and keeps a
constant state in the vicinity of the peak value until receiving a
stop command. When the emission of X-rays is stopped upon receiving
the stop command in the X-ray source 13, the radiation dose of
X-rays gradually decreases, and then becomes "0" to stop the
emission of X-rays completely.
In the first operating mode, the control unit 41 sets a threshold
of a total radiation dose of X-rays according to a request of
examination input through the console unit 24, namely, sex, age,
body part, purpose for imaging, and the like of a patient. When an
instruction for standby for imaging is input by the controller 23,
the control unit 41 sets the flat panel detector 36 in a standby
state. In the standby state, the control unit 41 causes the flat
panel detector 36 to carry out the resetting. As the first
operating mode is a mode selected in the case of communication
compatibility with the X-ray generating apparatus 11, a control of
start synchronization of the X-ray imaging assembly 21 is performed
in a well-known signal communication method. Specifically, the
control unit 41 receives an emission start signal via the
controller 23 upon being output by the radiation source control
assembly 14. The control unit 41, upon receiving the emission start
signal, turns off the TFTs 43 of the pixels 37 and changes over the
same from the standby state to the storage step. As the TFTs 43 are
turned off, the pixels 37 are caused to store the signal charge
according to the dose of the applied X-rays.
When the storage step is started in the first operating mode, a
total radiation dose of X-rays starts being measured. Even when the
TFTs 43 of the pixels 37 are turned off, the short-circuited pixels
62 are always short-circuited with the signal lines 48. The control
unit 41 can measure the total radiation dose of X-rays according to
an output of the short-circuited pixels 62 flowing to the signal
lines 48 while X-rays are emitted. The control unit 41 accumulates
the output voltage Vout of the short-circuited pixels 62, measures
the total radiation dose of X-rays, and compares a result of the
measurement with a threshold. When the total radiation dose of
X-rays reaches the threshold, the control unit 41 causes the
controller 23 to send a stop signal to the radiation source control
assembly 14. The radiation source control assembly 14 upon
receiving the stop signal sends the stop command to the X-ray
source 13 to stop emission of X-rays. Also, the control unit 41
terminates the storage step of the flat panel detector 36 at the
same time as sending of the stop signal, for changeover to the
readout step.
In the first operating mode described above, real-time processing
is required for communication to control the total radiation dose
of X-rays at high precision, in relation to a sync signal for time
points of an emission start and emission end of an emission start
signal and stop signal in communication between the X-ray imaging
assembly 21 and the radiation source control assembly 14 for the
sync control. Therefore, it is necessary to carry out communication
rapidly between the communication interface 33, the communication
interface 23a and the communication device 14c in the X-ray imaging
assembly 21, the controller 23 and the radiation source control
assembly 14. The communication interface 33, the communication
interface 23a and the communication device 14c are provided with
two communication modes, namely a high speed communication mode for
use in communication of a sync signal with which rapidity is
important, and a normal mode for use in communication with which
rapidity is not very important. The normal mode is used for sending
and receiving a command for instructing performance of a particular
task at the time of setting the apparatuses and operation control.
The command is a signal including binary information (0001, 1001
and the like) expressing meanings of various instructions. A task
of decoding is required for the received command for recognizing a
meaning of the command. As the normal mode is a communication mode
inclusive of the decoding, surplus time is required for decoding in
the process time.
The high speed communication mode is a mode in which decoding can
be omitted. Specifically, a sender sends a sync signal such as an
emission start signal and stop signal only with a pulse wave in the
high speed communication mode. A recipient receives the pulse wave,
detects edges of a rise and fall of the pulse wave and judges that
the sync signal is received. For example, the emission start signal
is a signal sent by the X-ray generating apparatus 11 to the X-ray
imaging apparatus 12, and is transmitted sequentially from the
communication device 14c of the X-ray generating apparatus 11 to
the communication interface 23a of the controller 23 and to the
communication interface 33 of the X-ray imaging assembly 21. The
communication device 14c sends a pulse wave to the communication
interface 23a as an emission start signal. The communication
interface 23a determines the emission start signal at the time of
detecting the rise of the pulse wave, and transfers the received
pulse wave to the communication interface 33. Also, the
communication interface 33 determines the emission start signal at
the time of detecting the rise of the pulse wave, and notifies the
control unit 41 thereof.
According to this, it is possible to omit the processing of
decoding in the normal mode. Rapid real-time communication is
possible. Note that an edge of the pulse wave is detected in the
high speed communication mode. However, it is possible to transmit
a command of an emission start signal expressed as binary
information instead of the pulse wave, and to detect an edge
included in the command. Also, it is possible in the high speed
communication mode to utilize a signal of light or sound besides
the electric signal for communication. Furthermore, although the
high speed communication mode is provided in each of the
communication interface 33, the communication interface 23a and the
communication device 14c for command communication, it is possible
to install a communication device in addition to the communication
interface 33, the communication interface 23a and the communication
device 14c for high speed communication specialized for the sync
signal.
As illustrated in FIG. 6, the second operating mode is a mode
selected in case of non-communicability with the X-ray generating
apparatus 11. The controller 23 and the X-ray imaging assembly 21
cannot receive an emission start signal from the X-ray generating
apparatus 11. Thus, the control unit 41 performs the control of
start synchronization and the control of stop synchronization
according to an auto-detecting method.
In the control of start synchronization, the control unit 41 in the
standby state measures a radiation dose of X-rays according to an
output voltage Vout corresponding to a signal charge generated by
the short-circuited pixels 62, and starts monitoring changes in the
radiation dose of X-rays. The control unit 41 compares the output
voltage Vout with a predetermined threshold Vth, and if the output
voltage Vout becomes higher than the threshold Vth, detects an
emission start of X-rays.
When the emission start of X-rays is detected, the control unit 41
turns off the TFTs 43 of the pixels 37 and changes over from the
standby state to the storage step in a manner similar to the first
operating mode. After the changeover to the storage step, the
control unit 41 starts the control of stop synchronization. Even
when the TFTs 43 of the pixels 37 are turned off, the
short-circuited pixels 62 are always short-circuited with the
signal lines 48. While X-rays are emitted, the control unit 41
continues monitoring changes in a radiation dose of X-rays
according to an output of the short-circuited pixels 62 flowing to
the signal lines 48. When a stop command is input to the X-ray
source 13 upon a lapse of the irradiation time set in the imaging
condition, intensity of X-rays starts decreasing. When the output
voltage Vout becomes equal to or less than the threshold Vth, the
control unit 41 detects a start of the decrease in the X-ray
intensity, and detects an emission end of X-rays. In response, the
control unit 41 terminates the storage step of the flat panel
detector 36 and changes over to the readout step.
The operation of carrying out of the first operating mode in the
X-ray imaging assembly 21 incorporated in the X-ray imaging system
10 of FIG. 1 is described by referring to a flow chart of FIG. 7. A
body part of the object H and the irradiation position of the X-ray
source 13 are set relative to the imaging stand 22 where the X-ray
imaging assembly 21 is set. An imaging condition is set in the
X-ray source 13, inclusive of a tube voltage, tube current,
irradiation time and the like. The console unit 24 inputs a request
of examination to the controller 23, namely, sex, age, body part,
purpose for imaging, and the like of a patient. The control unit 41
of the X-ray imaging assembly 21 sets a threshold for the total
radiation dose of X-rays according to the request of examination
(S101).
When the control unit 41 of the X-ray imaging assembly 21 is
supplied by the controller 23 with an input of instruction of
standby for imaging, the flat panel detector 36 (FPD as image
detector) changes over to the standby state (S102). When a start
command for emission is input to the X-ray source 13 by depression
of the radiation switch 15, the X-ray source 13 starts emission of
X-rays to the object H. At the same time, the radiation source
control assembly 14 sends an emission start signal to the
controller 23. The control unit 41, upon receiving the emission
start signal through the controller 23 (S103), starts the flat
panel detector 36 to operate for the storage step (S104).
During the storage step of the flat panel detector 36, the control
unit 41 accumulates the output voltage Vout, measures the total
radiation dose of X-rays (S105), and compares the total radiation
dose of X-rays with the threshold (S106). When the total radiation
dose of X-rays comes up to the threshold, the control unit 41 sends
a stop signal to the radiation source control assembly 14 through
the controller 23 (S107). The radiation source control assembly 14
upon receiving the stop signal sends a stop command to the X-ray
source 13 to stop emission of X-rays. At the same time as sending
of the stop signal, the control unit 41 stops the flat panel
detector 36 from the storage step, and sets the flat panel detector
36 for the readout step (S108). An X-ray image being read is
written to the memory 56 and transmitted to the console unit
24.
The operation according to the second operating mode is described
with reference to a flow chart of FIG. 9, the second operating mode
being selected when the X-ray imaging assembly 21 is combined with
an X-ray imaging system 65 having an X-ray generating apparatus 64
without a communicating function as illustrated in FIG. 8. Note
that the X-ray imaging system 65 is structurally the same as the
X-ray imaging system 10 of FIG. 1 except for a difference in that a
radiation source control unit 66 does not have the communication
device 14c and is incompatible with the controller 23 for the
communication compatibility. Elements in the X-ray imaging system
65 similar to those in FIG. 1 are designated with identical
reference numerals. Also, the second operating mode is selected
also in the case of communication incompatibility between the
communication device 14c of the X-ray generating apparatus 11 of
FIG. 1 and an interface of the X-ray imaging apparatus 12. The
operation of this construction is similar to that of FIG. 8.
In a manner similar to the first operating mode, the positioning of
the irradiation position, setting of an imaging condition,
inputting of a request of the examination, and the like are carried
out in the second operating mode. When a command for standby of
imaging is input to the control unit 41 of the X-ray imaging
assembly 21 by the controller 23, the flat panel detector 36 is
changed over to the standby state (S201). Upon changeover to the
standby state, the flat panel detector 36 starts resetting, and
starts measurement of a radiation dose of X-rays (S202).
When an emission start command is input to the X-ray source 13 by
depressing the radiation switch 15, the X-ray source 13 starts
applying X-rays to the object H. The flat panel detector 36
compares the output voltage Vout with the threshold Vth, and
monitors a change of a radiation dose of X-rays (S203). When the
radiation dose of X-rays increases to make the output voltage Vout
higher than the threshold Vth, then an emission start of X-rays is
detected (S204). As the emission start is detected, the flat panel
detector 36 turns off the TFTs 43 of the pixels 37 to start the
storage step (S205).
Even during the storage step, the flat panel detector 36 compares
the output voltage Vout with the threshold Vth to monitor a change
in the radiation dose of X-rays (S206). When the irradiation time
set in the imaging condition has elapsed, the X-ray source 13
receives an input of a stop command, so that intensity of X-rays
starts decreasing. When the output voltage Vout becomes equal to or
lower than the threshold Vth, the flat panel detector 36 detects a
start of the decrease of the intensity of X-rays, to determine an
emission end (S207). The control unit 41 terminates the storage
step of the flat panel detector 36 upon determining the emission
end, and starts the readout step (S208). An X-ray image being read
is written to the memory 56 and transmitted to the console unit
24.
As described heretofore, it is possible in the present embodiment
to select one of using methods of the short-circuited pixels 62
suitably according to communication compatibility or
incompatibility with the X-ray generating apparatus in the X-ray
imaging system having the X-ray imaging assembly 21. In case of the
communication compatibility with the X-ray generating apparatus, an
auto-detecting method is not required in sync control. The
short-circuited pixels 62 can be used for exposure control.
Consequently, overexposure of an X-ray image or overexposure to an
object can be prevented. In case of the communication
incompatibility with the X-ray generating apparatus, the
short-circuited pixels 62 are used for sync control in the
auto-detecting method. An X-ray imaging system can be constructed
by combining an X-ray generating apparatus known with an X-ray film
or IP plate, an X-ray generating apparatus with incompatibility of
a communication interface, for example, due to a difference in the
manufacturer, with the X-ray imaging assembly 21.
[Second Embodiment]
In the first operating mode of the first embodiment, a sync control
of a signal communication method for starting the storage step of
the flat panel detector 36 is performed in synchronism with an
emission start signal transmitted by the radiation source control
assembly 14. As illustrated in FIG. 10, an emission start of X-rays
from the X-ray source 13 can be detected by the short-circuited
pixels 62 in the first operating mode, so that the storage step of
the flat panel detector 36 can be started in synchronism therewith.
For this situation, the short-circuited pixels 62 are utilized for
both of the control of start synchronization and exposure
control.
In the second operating mode of the first embodiment, the storage
step of the flat panel detector 36 is terminated by detecting an
emission end of X-rays with the short-circuited pixels 62. However,
it is possible as illustrated in FIG. 11 to terminate the storage
step upon lapse of a predetermined time from the start of the
storage step. In this manner, it is possible in the second
operating mode to perform at least the control of start
synchronization. It is unnecessary to perform the control of stop
synchronization of the auto-detecting method of detecting the time
point of the emission end of X-rays. Also, the flat panel detector
may be previously set in the storage step by manual operation and
receive application of X-rays for imaging. For this structure, it
is possible to detect only the emission end without detecting the
emission start, and change over from the storage step to the
readout step. In the second operating mode, the total radiation
dose of X-rays can be measured so that the storage step of the flat
panel detector 36 can be terminated upon reach of the total
radiation dose to the threshold. As the transmission of a stop
signal to the X-ray generating apparatus 11 is impossible, the
irradiation of the X-ray generating apparatus 11 cannot be stopped.
A period of the storage step in the X-ray imaging assembly 21 can
only be adjusted.
In the first embodiment, the pixels 37 are reset while the flat
panel detector 36 is in the standby. However, it is possible to
carry out the resetting after detecting an emission start of X-rays
and then change over to the storage step, as illustrated in FIG. 12
for the exposure control and in FIG. 13 for the sync control. An
example of the resetting carried out at this time point may be the
sequential resetting or simultaneous resetting or total pixel
resetting. However, it is preferable to carry out the total pixel
resetting so that the resetting can be as short as possible.
[Third Embodiment]
As illustrated in FIG. 14, the imaging area 38 of the flat panel
detector 36 can be split into two partial areas 70 and 71 including
a central partial area 70 and a side partial area 71, the central
partial area 70 being disposed at a center, the side partial area
71 being disposed around the central partial area 70. The
short-circuited pixels 62 are disposed in the central and side
partial areas 70 and 71, which can be utilized discretely between
the exposure control and sync control.
For example, a radiation dose of X-rays applied to the flat panel
detector 36 by the X-ray source 13 is higher in the central partial
area than in the side partial area. Thus, the central partial area
70 is used for sync control. The side partial area 71 is used for
exposure control. Specifically, the control unit 41 performs the
sync control according to an output of the short-circuited pixels
62 disposed in the central partial area 70, and performs the
exposure control according to an output of the short-circuited
pixels 62 disposed in the side partial area 71. As the
short-circuited pixels 62 are connected with respectively the
signal lines L, the control unit 41 selects the central and side
partial areas 70 and 71 by selecting the signal lines L. At the
time of the sync control, the central partial area 70 with the
higher radiation dose of X-rays is used to detect an emission start
and emission end of X-rays with good precision. At the time of the
exposure control, the side partial area 71 is used to prevent an
error in the exposure due to underexposure, because the total
radiation dose is measured with X-rays of a lower radiation dose
than the central area.
In view of events of actual imaging, an object smaller than the
area size of the imaging area 38, such as a hand or foot, is likely
to be disposed at the center of the imaging area 38. The side area
is likely to be a through area to which X-rays are applied directly
without an object. For this situation, X-rays incident upon the
imaging area 38 are more in the side area than at the center. In
reverse to the embodiment of FIG. 14, it is preferable to use the
side partial area 71 for the sync control and to use the central
partial area 70 for the exposure control.
Fourth Embodiment
Also, sensitivity of pixels in a partial area for use in the
exposure control or sync control can be made relatively higher than
sensitivity in the remaining partial area not for use in the
control. For example, sync control is performed in a flat panel
detector having the central and side partial areas 70 and 71
illustrated in FIG. 14. The sensitivity of the short-circuited
pixels 62 of the central partial area 70 for use in the sync
control is set higher than that of the short-circuited pixels 62 in
the side partial area 71. At the time of the exposure control, the
sensitivity of the short-circuited pixels 62 of the side partial
area 71 for use in the exposure control is set higher than that of
the short-circuited pixels 62 in the central partial area 70.
Accordingly, it is possible to perform both of the exposure control
and sync control at high precision even for imaging with a low
radiation dose of X-rays. For example, a gain of an amplifier for
connection with the signal line L can be raised in order to change
the sensitivity. Also, it is possible to carry out binning to add
up outputs of a plurality of the short-circuited pixels 62 for
raising the sensitivity.
Note that partial areas are not limited to the two partial areas or
the central and side partial areas 70 and 71 to which the imaging
area is split as described above. The imaging area can be split
into three or more partial areas. A shape and area size of the
partial areas can be equal or can be different between those.
Furthermore, each one of the third and fourth embodiments can be
combined with the first embodiment. The X-ray imaging assembly 21,
if the X-ray generating apparatus 11 has communication
compatibility, is set in the first operating mode, in which the
sync control is performed in the signal communication method. The
short-circuited pixels 62 in the central and side partial areas 70
and 71 are used for the sync control in the second operating mode
and for the exposure control.
[Fifth Embodiment]
Although the above embodiments are described with imaging of a
still image, motion imaging can be carried out in the X-ray imaging
assembly 21, such as radiographic imaging. As illustrated in FIG.
15, a plurality of X-ray pulses are applied successively for
imaging as X-rays in a pulsed form in the motion imaging. In this
event, the control unit 41 detects a rise and fall of each of the
X-ray pulses with the short-circuited pixels 62 to detect time
points of emission of the X-ray pulses. The flat panel detector 36
can be changed over between the standby, storage step and readout
step in synchronism with the detected time points.
Also, it is possible in the control unit 41 to measure a radiation
dose with one X-ray pulse from the short-circuited pixels 62 in the
storage step, and control an output gain of the amplifier in the
readout step according to a result of the measurement. The gain
control can be performed by, for example, the integrating
amplifiers 49, or by amplifiers (not shown) connected with output
terminals of the integrating amplifiers 49 to amplify the voltage
signals D1-Dm. As the short-circuited pixels 62 are disposed in the
imaging area 38 discretely from one another, it is possible to
estimate the contrast of X-ray image according to outputs of the
short-circuited pixels 62 of different positions, to control the
output gain according to the estimated contrast.
In the above embodiments, the short-circuited pixels disposed in
the imaging area measure a radiation dose of X-rays. It is possible
to measure the radiation dose of X-rays accurately because the
short-circuited pixels are structurally the same as regular pixels
and have an equal sensitivity to X-rays. It is possible with high
precision to detect an emission start, emission end, and total
radiation dose. Owing to substantially the same structure, the
short-circuited pixels can be manufactured easily, with a small
increase in the manufacturing cost.
There are various forms of radiation detectors besides the
short-circuited pixels. For example, a bias voltage is applied to a
photo diode constituting a pixel. A bias current flowing in the
bias line is changed according to an amount of the signal charge
generated in the photo diode. A radiation dose of X-rays can be
measured by detecting the bias current. Even when the TFT of pixels
is turned off, a leak current of a low level flows in a signal line
according to an amount of the signal charge generated in the photo
diode. A radiation dose of X-rays can be measured by detecting the
leak current. In the methods of detecting the bias current or leak
current, a detector for detecting currents is the radiation
detector. Also, a radiation detector can be incorporated in an
X-ray imaging apparatus, inclusive of elements specialized for
detecting X-rays in a different form from the short-circuited
pixels. The elements can be disposed inside or outside the imaging
area. Also, an ionization chamber or other known radiation
detectors may be provided.
Also, although the flat panel detector of the TFT type in which the
TFT matrix substrate is formed by use of the glass substrate, a
flat panel detector may be constituted by use of a CMOS image
sensor or CCD image sensor in which a semiconductor substrate is
used. When the CMOS image sensor is used, the following merits are
obtained. It is possible by use of the CMOS image sensor to carry
out so-called non-destructive readout in which a signal charge
stored in pixels is read as a voltage signal through amplifiers in
connection with the pixels without flowing out of the signal charge
for the pixels to the signal lines for the readout step. So it is
possible even during the storage step to measure the strength of
X-rays by selecting any of the pixels in an imaging area and by
reading the signal charge from the pixel. Consequently, it is
possible in use of the CMOS image sensor to use any of the normal
pixels as a radiation detector for measurement of the radiation
dose without a special radiation detector for the measurement of
the radiation dose of X-rays in the manner of the short-circuited
pixels described above.
Furthermore, an X-ray imaging apparatus of the present invention
can have any one of various forms other than the above
embodiments.
The X-ray imaging apparatus is used for the X-ray imaging system
installed in an imaging room in a hospital, and also can be carried
in a medical cart which is used for moving between hospital rooms
and one room after another for the purpose of imaging, and also can
be adapted to a portable system which can be used for X-ray imaging
in a site requiring emergency medicine due to an accident, disaster
or the like or in a home of a patient receiving a health care
service at home.
In the above examples, the controller 23 for imaging is separate
from the X-ray imaging assembly. However, the controller 23 can be
a portion of a single machine including the X-ray imaging assembly.
For example, a function of the imaging controller can be
incorporated in a control unit of the X-ray imaging assembly.
In the above embodiments, the portable type of X-ray imaging
assembly has been described as examples. However, the present
invention is applicable to an installed type of X-ray imaging
assembly.
The present invention is also applicable to an imaging system for
use with gamma rays or other rays without limitation to X-rays.
Although the present invention has been fully described by way of
the preferred embodiments thereof with reference to the
accompanying drawings, various changes and modifications will be
apparent to those having skill in this field. Therefore, unless
otherwise these changes and modifications depart from the scope of
the present invention, they should be construed as included
therein.
* * * * *